In existing wells, the need arises to enhance production by drilling one or more laterals. Some of these wells are cased and are producing through the main wellbore. In some situations, it is desirable to resume production from below the lateral after the lateral is completed. At the same time, it is desirable to be able to isolate the wellbore below the lowermost lateral while the lateral is being drilled. The reason for this is that the formation below the lowest lateral can be adversely affected by hydraulic pressures brought on it from the drilling fluid gradient and/or equivalent circulating density. For that reason, it is advantageous to be able to isolate the wellbore below a whipstock, and at a later time allow flow to resume after the window exit has been created or at any point thereafter upon completion of the lateral or laterals.
In some situations, it is required to isolate the main bore while drilling the lateral or laterals above the window exit. The lateral may require the drilling fluid to be such that the fluid gradient would not control the main bore reservoir. In this situation, the main bore must be isolated. Upon completion of these uphole operations, the isolation or well control of the main wellbore is not required.
In the past, whipstocks have been available with a full or partially open bore therethrough for the purpose of allowing subsequent flow from below the whipstock from the main wellbore at the conclusion of milling of the window and drilling the lateral. However, these prior designs did not provide the ability to isolate the main wellbore below the whipstock during the milling of the window, the drilling of the lateral, or the insertion of a liner into the lateral.
Accordingly, an object of the invention is to be able to selectively provide communication from the main wellbore around the whipstock while leaving the whipstock in place. With the whipstock in place, it can be used to guide a liner into the lateral, while at the same time allow selectively the resumption of flow from the main wellbore to the surface. Another objective of the invention is to allow the opening of the main wellbore from below the whipstock to be accomplished in a variety of techniques. Some of these techniques include chemical attack through the dissolving of a plug, mechanically shifting a sleeve, or the use of signals from the surface communicated through the wellbore to the valve below the whipstock to actuate it when desired. These and other objectives of the present invention will be more readily understood by a review of the detailed specification which appears below.